Pharmaceutical companies are the ones who are most against legalization.
Say you patent a pill that your company makes. and upsell it to millions of people and make huge profits. Can you patent a natural plant that helps to treat and/or alleviate symptoms of that same illness? No. Theres no money in that.
Why should people buy your expensive medication for glaucoma treatment when you can grow a plant that better treats your illness for free?
Unlikley in the near future, In the short-run this would cost the company more in hiring botanical departments than to just send lobbyists to keep these kinds of bills from passing.
Its true that Marijuana is the #1 cash crop in America but you need to think of the people who are running these billion dollar industries. Old, rich white men who probably still view marijuana as taboo despite the obvios benefits its can provide.